1. Field of the Invention
The present invention relates to a color photographic process, particularly, to a process for stabilizing a color developing solution to improve preservability (storage capability) thereof and reduce the occurrence of fog or stain caused by long-term processing using a developing solution which has been permitted to stand in contact with air for a period of time, i.e., developing agent is oxidized by contact with the oxygen in the air, whereupon developing capability is lowered and color fog results.
2. Description of the Prior Art
In color photographic processes, a color photographic material produced by applying silver halide emulsions (containing or not containing couplers such as a cyan, yellow or magenta coupler) to a support is image-wise exposed to light and then subjected to a series of processings to reproduce a color image on the photographic material.
Fundamental steps in such processings comprise a color development and a desilvering. Namely, in the color development of the exposed silver halide color photographic material, exposed silver halide oxidizes a color developing agent while it is reduced to silver at the same time, and the oxidized color developing agent reacts with couplers to form a dye image. In the thus processed color photographic material, developed silver formed by the prior step is oxidized by the function of an oxidizing agent (called a bleaching agent) at desilvering and is removed from the photographic material by dissolving by means of a silver ion chelating agent (called a fixing agent). Consequently, only a dye image is left in the photographic material. An actual development processing usually comprises auxiliary steps for preserving the photographic and physical qualities of the image or for improving the preservability of the image in addition to the above described two fundamental steps, that is, the color development and the desilvering. There are, for example, steps such as hardening for preventing excess softening of sensitive layers during processing, stopping for effectively stopping the development reaction, image stabilization for stabilizing the image and defilming for removing a backing layer on the support. Such color photographic processing has been commonly used since 1940.
In addition to the above described processings, there are color intensifying processings as have been described in detail in, for example, The Theory of the Photographic Process written by C. E. K. Mees, 2nd Edition, Chapter 25, U.S. Pat. No. 3,674,490 and Japanese Patent Application Nos. 9728/73 and 9729/73.
Fog generally occurs in color photographic sensitive materials when they are subjected to color development. Such fog is called "development fog"; the occurrence of such fog can be prevented by adding halides such as potassium bromide or potassium iodide or organic anti-fogging agents such as 1-phenyl-5-mercaptotetrazole, benzotriazole or 5-nitrobenzimidazole, etc., to a developing solution. However, apart from development fog, fog also occurs due to the use of color developing solutions which has been permitted to stand in contact with the air for extended periods of time, as earlier described. Such fog is called "color fog" or "stain", and the occurrence of such fog cannot be prevented by adding the above described halides or organic anti-fogging agents (hereinafter, "fog" in this specification means color fog or stain, unless otherwise indicated).
The occurrence of fog increases with elevated development temperatures and it becomes particularly remarkable when processing at a high temperature of above 30.degree. C. It is believed that one cause of fogging is a deterioration of the color developing solution which is accelerated by elevated development temperatures. Accordingly, the occurrence of fog is closely related to the preservability of the color developing solution, and it is believed that a main cause of fogging is due to oxidation products formed by a partial oxidation of the color developing agent included in the color developing solution with the passage of time. As such oxidation products of the color developing agents, there are oxidants (semiquinone or quinonediimine) of the color developing agents, quinonemonoimines formed by a deamination reaction, oxidants thereof, and quinonemonoimine-sulfuric acid addition products, etc. On the other hand, hydrogen peroxide is a by-produced peroxide. Among these oxidation products, some of them react with couplers in the sensitive material to form dyes, whereby fog is caused. Further, it is believed that fog is also caused by the hydrogen peroxide. In any case, these compounds bring about fog in unexposed areas of the color photographic material. On the other hand, such fog appears not only in unexposed white areas where dyes should not be formed, but also the occurrence of fog in unexposed layers brings about stain when, for example, only one or two layers among the photographic emulsion layers in the sensitive material are exposed to light. For example, in the case that only a red-sensitive layer is exposed to light, fog occurs in a green-sensitive layer and a blue-sensitive layer to cause some degree of magenta and yellow coloring, whereby a cyan color image having low purity is formed.
This color fog in the white areas and stain in the color image areas brings about a remarkable deterioration in the quality of the photographic image.
Usually, a sulfite or a water soluble salt of a sulfite and hydroxylamine is added to a color developing solution in order to improve preservability. In the case of using sulfite only, though preservability is somewhat improved, fog remarkably occurs. On the other hand, in the case of using the water soluble salt of a sulfite and hydroxylamine, the preservability of the developing solution is remarkably improved and it is possible to reduce the occurrence of fog caused by the elapsed developing solution.
It has been reported, however, that hydroxylamines are injurious to humans (The Merck Index--An Encyclopedia of Chemical and Drugs by P. G. Stecher, 8th Ed. (1953)). In the Pharmacopoeia of Japan, hydroxylamine and water soluble salts thereof are designated as poisonous substances. They are difficult to handle because of the danger when they are handled by amateurs.
Recently, many preservatives have been suggested other than hydroxylamines. For example, 2-anilinoethanol (U.S. Pat. No. 3,823,017) and dihydroxyalkenes (U.S. Pat. No. 3,615,503) have been suggested. However, both 2-anilinoethanol and dihydroxyalkenes have insufficient stability and do not show an anti-fogging effect.